Cellular communication networks, or cellular networks, comprise a large number of cells which are integrated to form the network. A cellular network may span an entire country, in which case it may be referred to as a countrywide network. Cellular networks provide large-area roaming, allowing users to move about large areas with continuous access to the network. This makes possible, for example, for a consumer to remain connected to a single voice call or data connection while traversing a country by train or car.
Networks with smaller geographical reach may be referred to as local networks. Whereas local networks may not be able to offer the geographic reach of cellular networks, especially nationwide cellular networks, they may offer a high datarate in a more limited area where large numbers of customers need connectivity. One example of a local network is a wireless local area network, WLAN, access point. Another is a femtocell, by which is meant a cellular cell of limited range.
Femtocells, or in general cells with smaller cells, may be deployed for various reasons. Historically smaller cells have been used to increase network capacity by allowing frequencies to be re-used to a higher degree over a given geographic area. A large cell allows for a set of frequencies to be used only once, which limits capacity. By splitting a large cell into smaller ones, the same set of frequencies may be used more than once, allowing a network operator to serve a larger number of subscribers in the same area and by using the same frequency band. Other names for smaller cells include picocells which may be seen as larger than femtocells, and microcells which in turn may be seen as larger than picocells.
Smaller cells may also be used where transmission power limits don't allow installing a cell of larger radius. This is due to the fact that a base station serving a large cell must transmit to the edge of the large cell, which is farther away than an edge of a smaller cell.
Another reason for using smaller cells is to allow a limited subset of subscribers to access an alternative cell, which may be comprised in a larger network that is open to a larger set of subscribers. Such a cell may be known as a closed subscriber group, CSG, cell. To define a CSG cell, a corresponding set of subscribers that have access to the cell may be defined. A CSG cell may be considered to be a special type of femto- pico- or microcell, for example.